List of fictional alien species: Y
| Name | Source | Type |
|---|---|---|
| Y5 | Adventure Time: Distant Lands | Rabbit-like humanoid |
| Yacatisma | Church of the SubGenius | |
| Yag-Kosha | Robert E. Howard's The Tower of the Elephant | Humanoid elephant |
| Yaetuans | Christan Clines's The Yaetuan Sagas | Six limbed intelligent species |
| Yanme'e | Halo | |
| Yautja | Predator | Humanoid. Also known as Predators. They are a warrior race that hunts down other sentient races for sport, but follow a code of honor and deeply respect those who manage to defeat one of their own in combat. |
| Yariru | Vampire Idol | Vampire-humanoids |
| Yazirian | Star Frontiers | Ape-like humanoid glider |
| Yeerks | K. A. Applegate's Animorphs | Slug-like parasites. They need a host to see, walk, and communicate, and are the main antagonists of the Animorphs series, intent on enslaving other species. |
| Yehat | Star Control | Pterodactyl-like |
| Yeti | Doctor Who | |
| Yilane | West of Eden series by Harry Harrison | |
| Yip-Yips | Sesame Street | |
| Yliis | 2300 AD | |
| Yolkians | Jimmy Neutron | Gooey Slug-like aliens with egg shaped suits. |
| Yomingans | Schlock Mercenary | |
| Yor | Galactic Civilizations | |
| Yorn | Star Control 3 | |
| Ythrian | Poul Anderson's Technic History | Eagle-like aliens |
| Yridian | Star Trek | |
| Yugopotamians | The Fairly OddParents | Squid-like aliens with dome-covered brains. |
| Yuuzhan Vong | Star Wars | Humanoid |